Multiple-bulb fluorescent lighting fixtures have become extremely popular for providing illumination of relatively wide expanses of space in large rooms, such as encountered in factories, offices, stores, and the like. These lighting fixtures have gained widespread acceptance because of the significantly reduced costs of operating them as contrasted with incandescent light fixtures and, further, because of the generally non-glare and even distribution of light which can be obtained from such fixtures. Even so, fluorescent lighting fixtures in common use today are relatively inefficient. Generally, these fixtures employ translucent covers or the like over the fluorescent bulbs to disperse the light and spread it more evenly in the area to be illuminated. Obviously, if a translucent cover is placed over the fixture, a substantial loss of lighting efficiency occurs simply by virtue of the use of such a cover.
In addition, the housings for most fluorescent lighting fixtures, which use bulbs in the form of relatively long tubes on the order of four feet (4') in length, do little toward recovering and utilizing the light which is directed from the bulb onto the back and sides of the housing itself. The housings generally are of flat, rectangular configuration and they are painted white, which serves to reflect some of the light back out into the room. At the same time, however, much of the light emanating from the bulbs in multiple-bulb fixtures is directed directly from one bulb to another, or is reflected from the back of the fixture housing into the same or another bulb. All of this is wasted energy, which results in a reduced light output from the maximum which could be obtained from such a fixture. In addition, the light and heat which is reflected from the housing back into the bulbs tends to raise their temperature; and, as is well known, this in turn reduces the overall efficiency of operation of the bulbs.
In the past, some recognition of the inefficiency of standard fluorescent light fixtures has been noted and attempts have been made to increase the efficiency of the light output from such fixtures by placing between adjacent bulbs of multiple-bulb fixtures an inverted V-shaped elongated reflecting surface. Such an effort at increased efficiency is disclosed in the patents to Bodian et al, U.S. Pat. No. 2,864,939, issued Dec. 16, 1958, and Akely et al, U.S. Pat. No. 2,914,657, issued Nov. 24, 1959. Both of these fixtures are ceiling-type fixtures for directly lighting the room below, or the area below as in the case of Akely. The V-shaped reflectors, which are placed between the bulbs of these fixtures, do assist in recovering and spreading light which ordinarily would be lost in a conventional fixture not having the inverted V reflector units in it. A substantial amount of light and heat energy, however, is directed back into the bulbs in both of these fixtures; because the reflector placed behind the bulbs is the conventional flat surface used in most such fixtures. Thus, any light directed generally downwardly from the bulbs is reflected back into the bulbs. This light energy is lost and increases the temperature of the bulbs which, in turn, also reduces their efficiency. In addition, it also should be noted that the fixtures disclosed in both of these patents require a translucent cover to evenly disperse the light emanating from the fixtures since this is not accomplished by the shape of the reflectors themselves.
Another multiple-bulb or multiple-tube fluorescent lighting fixture utilized in a very specialized environment for lighting storefront show windows is disclosed in the patent to Campen, U.S. Pat. No. 2,335,735, issued Nov. 30, 1943. This fixture is designed with a stairstep-shaped reflector having an apex or point beneath each of the elongated bulbs of a multiple-bulb fixture in which the bulbs are relatively tightly packed together. Space-to-space distance between the bulbs, as shown in this patent, is less than the diameter of the bulbs themselves. There are no inverted V-shaped reflectors between adjacent bulbs in this fixture. From an examination of the shape of the reflector and the relatively close spacing of the bulbs, it is apparent that most of the light that is reflected from the bulbs onto the reflector behind them is reflected back into the bulbs themselves. The primary source of light from the fixture of Campen is direct light from the bulbs.
Single bulb fluorescent fixtures with enhanced reflectors for dispersing a more or less uniform pattern of light from the fixture are disclosed in the patents to Welch, U.S. Pat. No. 2,194,841, issued Mar. 26, 1940, and Netting, U.S. Pat. No. 2,323,073, issued June 29, 1943. The Welch patent discloses the placement of an inverted V-shaped reflector behind the single bulb with adjacent surfaces located to reflect the light from these surfaces onto other surfaces and direct it outwardly from the fixture. Much of the light from the bulb in the Welch reflector undergoes two (2) or three (3) reflections before it exits from the fixture. Consequently, there is a substantial loss of lighting efficiency as a result of the multiple reflections. The desired object of spreading the light which leaves the fixture is obtained at the cost of this reduced efficiency.
The Netting fixture employs a plurality of elongated reflective strips on each side of the single bulb used in the fixture with the strips being generally oriented in a concave curve cross-sectional configuration. In Netting, as in Welch, much of the light which issues from the half of the bulb facing the reflector undergoes multiple reflections resulting in reduced efficiency. As a consequence, the angular arrangement of the various reflecting surfaces results in a considerable reduction in the amount of light which issues from the fixture over that which could be obtained from a fixture minimizing the multiple reflections.
All of the above patents also are directed to light fixtures which are intended to be placed above the surface to be illuminated. In many installations, particularly commercial installations, indirect lighting is preferred. To maximize the efficiency of indirect lighting, it is desirable to have the fixture located near the ceiling, above the line of sight, with as wide as possible even light dispersion from the fixture. Furthermore, it is desirable to provide such a fixture which maximizes the amount of light reflected out of the fixture from each bulb of the fixture, if a multiple-bulb fixture is employed, and which provides a uniform illumination on the ceiling without requiring a translucent dispersing cover. An increase in even ten percent (10%) of the efficiency of such a fixture over standard fixtures would result in considerable savings in energy over the lifetime of operation of such a fixture.